1. Field of the Invention
The present invention relates to a disk reading apparatus for detecting a signal recorded along tracks of a disk by using a pickup such as a CD-ROM drive or a DVD player, and more particularly to a disk reading apparatus for changing a hysteresis width of a binarizing means that binarizes a tracking error signal with the hysteresis width according to tracking operation or track-jump operation.
2. Description of the Related Art
A CD-ROM drive, a DVD player, and the like are designed so that, in the case where data intended for replay are recorded on a track being different from the track being followed by a pickup, track-jump can be implemented. On the other hand, it is necessary to count the number of jumped tracks when the track-jump is implemented. Owing to this, there is provided a binarizing means for binarizing a tracking error signal with a predetermined hysteresis width. Then, the number of the jumped tracks is counted by counting a pulse appearing in a track count signal being an output from the binarizing means.
Moreover, the above-mentioned binarizing means is designed so as to implement binarizing with the same hysteresis width as usual even during the tracking, and the generated track count signal is also used for judging whether or not a turbulence occurs in a tracking servo. That is to say, if there is a scratch on a recording surface of the disk, it becomes impossible to keep causing the pickup to follow the track, and there occurs a situation where a detecting position of the pickup misses the track. Moreover, if an external shock is given to the apparatus during the tracking, it becomes impossible for the pickup to follow the track due to the shock. Then, when such a situation occurs, a greater level-change occurs to the tracking error signal, and level inversion occurs to the track count signal. Owing to this, the CD-ROM drive is designed so as to, if the level inversion occurs to the track count signal while the data are being read, read the data on the same track once again. Moreover, the DVD player for picture images is designed so as to stop the replay of the data in the same situation (it is indicated as the first prior art).
Moreover, in the prior art proposed as Japanese Patent Application Laid-Open Publication No. HEI 4-95227, there is disclosed a structure wherein a level set circuit for fixing an output level of an amplification circuit by controlling a gain of the amplification circuit of the tracking error signal. Accordingly, in the case where this technique is used, even when an optical disk comprising two areas (a pre-format area and a memory area) with different levels of the tracking error signal is replayed, the tracking error signal with a fixed level can be gained in both of these two areas. Owing to this, the tracking can be implemented with a high precision in both of the pre-format area and the memory area. Moreover, even when the track-jump between the pre-format area and the memory area is implemented, the tracking error signal controlled so as to have the fixed level is given to a drive circuit for causing the pickup to track-jump (it is indicated as the second prior art).
However, using the first prior art has had problems described below. That is to say, due to an unevenness and the like in formation of the disk, there occurs a situation where the level of the tracking error signal is greater in one disk, and the level of the tracking error signal is smaller in other disk. Owing to this, in the case where the track-jump is implemented on the disk with a smaller level of the tracking error signal, there are the cases where the level of the tracking error signal does not exceed the hysteresis width. When such a situation occurs, the number of the jumped tracks is counted as less than the actual number, and the actual number of the jumped tracks becomes greater than the intended number of the tracks.
On the other hand, if the hysteresis width for implementing binarizing is narrowed-down, a track count signal is correctly generated when the pickup crosses the tracks even on the disk with the smaller level of the tracking error signal. However, in the case where the hysteresis width for binarizing is narrowed-down, there occur the problems described below.
That is to say, if the degree of a disturbance given to the apparatus is low or the scratch on the recording surface is minute, the pickup can follow the track without missing the track. However, a small level change occurs to the tracking error signal at this time. On the other hand, the binarizing means implements binarizing with the same hysteresis width as that during the track-jump even during the tracking. Accordingly, if the hysteresis width is narrowed-down, the binarizing means inverts the level of the track count signal even for the above-mentioned small level change. As a result, in the case of the CD-ROM drive, even when the disturbance is within a degree whereat the pickup can continue to follow the track, the data of the same track is read once again regarding that a turbulence occurs in the tracking servo. Owing to this, a time for reading the data becomes longer. Moreover, in the DVD player for picture images, even a small disturbance can stop the replay.
Moreover, although there is disclosed in the second prior art a structure wherein an output level of the amplification circuit is fixed by controlling the gain of the amplification circuit for amplifying the tracking error signal, nothing is mentioned concerning the track count signal. Owing to this, it is difficult to adopt this technique to the case of the apparatus for implementing control based on the track count signal.
The present invention is created in order to solve the above-mentioned problems, and an object thereof is to provide the disk reading apparatus that can prevent an error on counting the number of the jumped tracks from occurring even concerning the disk with the smaller level of the tracking error signal without causing the error on detecting the turbulence in the tracking servo by changing the hysteresis width for implementing binarizing for generating the track count signal according to whether the pickup is caused to follow the track on the basis of the tracking error signal or the track-jump is implemented.
In order to achieve the object, according to the present invention, there is provided a disk reading apparatus comprising a pickup for detecting data recorded along a track of a disk by using a light, a binarizing means for transmitting a track count signal resulting from binarizing a tracking error signal generated on the basis of an output from the pickup, with a hysteresis width, a servo means for causing the pickup to follow the track on the basis of the tracking error signal, a jump means for causing the pickup to track-jump to an intended track by counting the number of jumped tracks on the basis of the track count signal, and a malfunction detecting means for transmitting a malfunction signal that indicates a malfunction of tracking in the case where level inversion occurs to the track count signal while the servo means is causing the pickup to follow the track, and it comprises a control means for widening the hysteresis width when the servo means causes the pickup to follow to track, and for narrowing the hysteresis width when the jump means causes the pickup to track-jump.
That is to say, in the case of the disk with the smaller level of the tracking error signal, a width of the level change of the tracking error signal while the pickup is crossing the tracks is narrower. However, since the hysteresis width of the binarizing means is narrow at this time, a pulse appears in the track count signal every time the pickup crosses the tracks. Moreover, in the case of the disk with the greater level of the tracking error signal, even when there occurs the turbulence of the tracking within a range where the error on the data reading is not made, a level change with a proper width appears in the tracking error signal. However, the hysteresis width of the binarizing means becomes wide at this time so that the inversion of the level does not occur in the track count signal.